This past week, I've been having constant problems with my 2007 Aluminium iMac (2.4GHz, 3GB memory, 320GB HDD). I've been downloading using Transmission, and when (sometimes) stopping or starting a download, my Mac would hang to a state where the Force Quit dialog would not even activate, it would then stay in this state for as long as I let it. I had to force restart every time. After a few force restarts, it lost its start-up disk, and it takes longer than usual to boot up.

I got scared a bit and started backing up the HDD to an external last night. I was busy playing music in iTunes while backing up when I observed the following:

Music would stop playing for a few seconds

The beach ball would start spinning during this time

Data transfer to the external drive would pause

And I would hear a very soft spinning sound in the background, a repeating noise which leads me to believe the HDD is struggling to read/write.

Obviously the HDD has some sort of problem, however, rather than assuming it's failing, can I fix it in some way? Could it be a cache error or file system corruption which can be fixed with a clean install of Snow Leopard? Any way I can fix this without having to buy a new HDD?

BTW. I have run both Repair Permissions & Verify Disk multiple times on this drive, and Verify Disk always returns a green message which states the HDD is fine. Also, S.M.A.R.T. status shows as Verified in Disk Utility.

Clone the boot drive using Carbon Copy Cloner or SuperDuper! and boot from the external to see if it suffers from the same problem. That will determine if it's a software problem (i.e. something running in the background) or a drive problem (either corruption or failing drive).
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EmmEffOct 17 '11 at 13:46

I had a VERY similar problem a few weeks ago. I backed up and did a clean install of the OS and everything is back to normal. I'd say to give that a shot.
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Matt RockwellOct 17 '11 at 17:04

4 Answers
4

Your own advice is fairly good in this scenario.
There is a possibility that you have just some serious file system corruption, but usually Disk Utility should catch that. If you want, you can boot into single user mode (CMD S on boot) and it will give you a little file system cleanup command you can run
fsck -fy and then press enter, when it finishes you reboot.

If this doesn't help, reinstalling after performing a backup is not a bad idea because it will isolate it to a software or hardware issue. The hard drive going over some area repeatedly could be just file system screw ups, but usually repeated noises are a bad sign for a hard drive, clicking etc.

If the problem comes back after the reinstall you definitely want to look into a new hard drive. Four years is not an uncommon life span for some hard drives.

Also just a quick point of clarification, the S.M.A.R.T status doesn't predict all failures, it just presages specific ones it can determine. Just because it isn't telling you your drive is failing doesn't mean it wont. Keeping everything backed up is a really good idea at this point.

It's worth noting that reinstalling the OS is a pretty disk intensive task. In my time I have seen a fresh install finish off a drive that was already failing or about to fail.
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macacoOct 17 '11 at 14:02

Yeah good point macaco, and that is why its important to always have a backup!
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hobsOct 18 '11 at 0:19

Thanks hobs. I will definitely try your suggestions when I get a go at my home iMac again, at the moment very busy and have a MBP to work on.
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Anriëtte MyburghOct 18 '11 at 6:59

I'm pretty convinced that this is a case of a dying drive. All the signs are there.

The best thing you can do is get as much data off as possible and then get your machine repaired at an Apple store or authorised service provider. Unfortunately a HD swap on an alu iMac is neither entirely trivial or fun.

During the backup process I'd recommend not using the computer for anything else and closing all unnecessary apps and background apps/services.

You are clearly aware of the issues involved and potential solutions. For the safety of your data I would recommend 2 additional things you can do.

A disk which makes unexpected noises is probably failing. The failure may happen soon or take some time. Nevertheless, it's always best to assume the worst, to check you backups work and to get a replacement as soon as possible. S.M.A.R.T. is useful although a random check may not show a problem. For continual monitoring and visible notifications of S.M.A.R.T. status, you should consider installing a utility such as SMARTReporter.

Memory, especially cheaper memory, isn't always reliable. Checking for memory problems is best done when you first get a new computer, and whenever you upgrade or install new memory. Of course, with the issues you describe, this is also a good time to investigate further. The most common method is to use one of the available memtest applications. There are commercial and free versions available. Free versions include:

I think this issue was due to a faulty memory DIMM. The original 1gig that came with the computer was starting to give in, I determined this by first removing the 2gig DIMM (3rd party memory installed). The computer then worked for a few hours without any hassles, but the hanging started up again after I did some stuff on it. I then switched the 1gig for the 3rd party 2gig, and then started up without any problems or hangs. I presume the 1gig was starting to give in and that was what was causing all the beach balls and hangs.

Thanks for all the suggestions. But I hope this was the issue, as I'm no longer having any issues.